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<title>跨域和缓存</title>
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<h1 id="-">跨域和缓存</h1>
<h2 id="cors-">CORS跨域</h2>
<p>搭建服务端：</p>
<p><strong><code>server.js</code></strong></p>
<pre><code>const http = require(&#39;http&#39;);
const fs = require(&#39;fs&#39;);
http.createServer((request, response) =&gt; {
  console.log(&#39;request come&#39;, request.url);
  const html = fs.readFileSync(&#39;index.html&#39;, &#39;utf8&#39;);
  response.writeHead(200, {
    &#39;Content-Type&#39;: &#39;text/html&#39;
  });
  response.end(html);
}).listen(8888);
console.log(&#39;server listening on 8888&#39;);
</code></pre><p><strong><code>server2.js</code></strong></p>
<pre><code>const http = require(&#39;http&#39;);
http.createServer(function (request, response) {
  console.log(&#39;request come&#39;, request.url);
  response.writeHead(200, {
    &#39;Access-Control-Allow-Origin&#39;: &#39;*&#39;,
    &#39;Access-Control-Allow-Headers&#39;: &#39;x-Test-Cors&#39;,
    &#39;Access-Control-Allow-Methods&#39;: &#39;POST,PUT,Delete&#39;,
    &#39;Access-Control-MAX-AGE&#39;: &#39;1000&#39;
  });
  response.end(&#39;123abc&#39;)
}).listen(8887);
console.log(&#39;server is listening on 8887&#39;);
</code></pre><p><strong>AJAX请求</strong></p>
<pre><code>var xhr = new XMLHttpRequest();
xhr.open(&#39;GET&#39;, &#39;http://127.0.0.1:8000&#39;);
xhr.send();
</code></pre><p><strong>JSONP</strong></p>
<pre><code>&lt;script src=&quot;http://127.0.0.1:8000&quot;&gt;&lt;/script&gt;
</code></pre><p>在<code>script</code>、<code>link</code>、<code>img</code>标签的<code>src</code>加载链接，此链接访问服务器的请求，并且返回可执行代码。</p>
<h2 id="cors-">CORS预请求</h2>
<p>我们不能通过设置<code>Access-Control-Allow-Origin</code>来解决所有的跨域问题。</p>
<p><strong>CORS其他限制</strong></p>
<ul>
<li>默认允许的方法只有：<code>GET</code>、<code>HEAD</code>、<code>POST</code></li><li>默认允许的<code>Content-Type</code>：<code>text/plain</code>、<code>multipart/form-data</code>、<code>application/x-www-form-urlencoded</code></li><li>默认允许的请求头：<code>Accept</code>、<code>Accept-Language</code>、<code>Content-Language</code>、<code>multipart/form-data</code>、<code>text/plain</code></li></ul>
<p>添加<code>&#39;Access-Control-Allow-Headers&#39;: &#39;x-Test-Cors&#39;</code>查看<code>network</code>面板会发现比之前多了一个请求，它的<code>Request Method</code>是<code>OPTIONS</code>。通过<code>OPTIONS</code>请求获得服务端的允许，然后再实际发送<code>POST</code>请求。</p>
<h2 id="-cache-control-">缓存头<code>Cache-Control</code></h2>
<p><strong>可缓存性</strong>，<code>public</code>、<code>private</code>、<code>no-cache</code></p>
<p><strong>到期</strong>，<code>max-age=&#39;&lt;second&gt;&#39;</code> 、<code>s-maxage=&#39;&lt;second&gt;&#39;</code>代理服务器、<code>max-stale=&#39;&lt;second&gt;&#39;</code>浏览器，发起端</p>
<p><strong>重新验证</strong>，<code>must-revalidate</code>、<code>proxy-revalidate</code></p>
<p><strong>浏览器缓存</strong></p>
<pre><code>const http = require(&#39;http&#39;);
const fs = require(&#39;fs&#39;);
http.createServer((request, response) =&gt; {
  console.log(&#39;request come&#39;, request.url);

  if (request.url === &#39;/&#39;) {
    const html = fs.readFileSync(&#39;index.html&#39;, &#39;utf8&#39;);
    response.writeHead(200, {
      &#39;Content-Type&#39;: &#39;text/html&#39;
    });
    response.end(html);
  }

  if (request.url === &#39;/script.js&#39;) {
    response.writeHead(200, {
      &#39;Content-Type&#39;: &#39;text/javascript&#39;,
      &#39;Cache-Control&#39;: &#39;max-age=200,public&#39;
    });
  }
  response.end(&#39;console.log(&quot;script loaded twice&quot;)&#39;)

}).listen(8888);
console.log(&#39;server listening on 8888&#39;);
</code></pre><h2 id="-">资源验证</h2>
<p><strong>浏览器</strong>-创建请求-&gt;<strong>本地缓存</strong>—&gt;代理缓存—&gt;源服务器</p>
<p>验证头：</p>
<p><code>Last-Modified</code>上次修改时间，配合<code>If-Modified-Since</code>或者<code>If-Unmodified-Since</code>使用</p>
<p><code>Etag</code>数据签名，配合<code>If-Modified</code>或者<code>If-Non-Match</code>使用、对比资源的签名判断是否使用缓存</p>
<pre><code>http.createServer((request, response) =&gt; {
  console.log(&#39;request come&#39;, request.url);

  if (request.url === &#39;/&#39;) {
    const html = fs.readFileSync(&#39;index.html&#39;, &#39;utf8&#39;);
    response.writeHead(200, {
      &#39;Content-Type&#39;: &#39;text/html&#39;
    });
    response.end(html);
  }

  if (request.url === &#39;/app.js&#39;) {
    const etag = request.headers[&#39;if-none-match&#39;];
    if (etag === &#39;777&#39;) {
      response.writeHead(304, {
        &#39;Content-Type&#39;: &#39;text/javascript&#39;,
        &#39;Cache-Control&#39;: &#39;max-age=20000000,no-cache&#39;,
        &#39;Last-Modified&#39;: &#39;123&#39;,
        &#39;Etag&#39;: &#39;777&#39;
      });
      response.end(&#39;123&#39;)
    } else {
      response.writeHead(200, {
        &#39;Content-Type&#39;: &#39;text/javascript&#39;,
        &#39;Cache-Control&#39;: &#39;max-age=20000000,no-cache&#39;,
        &#39;Last-Modified&#39;: &#39;123&#39;,
        &#39;Etag&#39;: &#39;777&#39;
      });
      response.end(&#39;console.log(&quot;script loaded twice&quot;)&#39;)
    }
  }
}).listen(8888);
</code></pre><h2 id="-cookie-session-"><code>cookie</code>和<code>session</code></h2>
<p>通过<code>Set-Cookie</code>设置，下次请求会自动带上，键值对，可以设置多个</p>
<p><strong><code>cookie</code>属性</strong></p>
<ul>
<li><code>max-age</code>和<code>expires</code>设置过期时间</li><li><code>Secure</code>只在<code>https</code>的时候发送</li><li><code>HTTPOnly</code>无法通过<code>document.cookie</code>访问</li></ul>
<pre><code>response.writeHead(200, {
  &#39;Content-Type&#39;: &#39;text/html&#39;,
  &#39;Set-Cookie&#39;: [&#39;id=123;max-age=2&#39;, &#39;abc=456;HttpOnly&#39;]
});
</code></pre>
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